Cholesteric liquid crystals (CLCs) possess a naturally occurring helical structure that produces striking reflective coloration. The inherent electrical response of the chiral nematic phase is limited, but through the use of polymer stabilization novel electrically driven optical properties can be accessed. Polymer stabilized cholesteric liquid crystals (PS-CLC’s) are formed by polymerizing reactive liquid crystals that have been doped into the chiral nematic liquid crystal. These PS-CLCs demonstrate a range of unique optical behaviors when subjected to electric fields, such as shifting colors and variations in spectral bandwidth. These phenomena are linked to the electrical manipulation of the polymer matrix and the corresponding reaction of the surrounding non-reactive liquid crystals. In this talk, we discuss our latest findings in this field, focusing on uncovering the underlying mechanisms of the electrically induced responses and applying these insights to enhance the performance of these materials.
Photoalignment of azobenzenes is one of the most versatile tools for liquid crystal self-assembly for both the surface and bulk. An azobenzene component is homogenously mixed with a liquid crystal and irradiated with polarized visible light. By utilizing a simple two-step exposure method, we can induce photoalignment on the front and back of the liquid crystal sample independently. This back to front alignment, if varying in LC director orientation, translates into a twist through the bulk. In this talk, we discuss the two-step exposure method and how to control the twist as well as introduce characterization methods on twist quantification.
This presentation reveals the re-writability property of azobenzene liquid crystal photoalignment. Stable in thermal fluctuations, one can change existing photoalignment by exposing it to polarized light in the visible regime. One can use this unique property by patterning photoalignment through the liquid crystal bulk in that the sample’s front and back have differing director orientations. Photoalignment using linear polarized light as well as complex polarizations will be covered. No surface alignment on sample substrates is necessary because the azobenzene is mixed with the liquid crystal in-situ in sample preparation.
Surface photoalignment has been utilized to control the liquid crystalline (LC) orientation by exposing the photosensitive surface coatings to linearly polarized light. However, there are limitations in cell thickness and director orientation complexity if surface photoalignment was conducted. An alternative approach in controlling the director orientation is bulk photoalignment. Azobenzenes, which have been used for surface photoalignment due to fast reorientation during exposure, are homogeneously mixed into a nematic LC. We present results on how azobenzene doped LCs can be aligned in various standard orientations. In addition, rewriting alignment and patterning complex director orientations via bulk alignment will be discussed.
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